A Planar Technology Primer

MAD's Planar Technology Primer...

If you're younger that 30, it probable that the term "planar transducer" is not part of your vocabulary. And likewise, unless you studied physics in college, the concepts of "planar theory" would be equally foreign to you.

Planar magnetic technology was first developed in the 1920's during the same decade that conventional cone speakers were created. Limitation with manufacturing techniques and raw materials stunted the growth of planar speakers and as a result, cone and compression speakers garnered the attention of the emerging professional audio industry. During the 1970's and '80's, planar technology began appearing in the high-end home stereo systems. Although the sound quality was extraordinary, there were significant issues that limited the use of this technology in the professional market. The transducer's efficiency was to low and the production costs were too high to justify mass production. In 1998, HPV Technologies research team broke through these barriers introducing the A-9 planar magnetic system to the pro-audio industry.

Planar research has continued into the development of systems for the US military and law enforcement agencies, public transportation systems, the maritime industry, and emergency mass notification.

So with that brief history, here's a simple primer on the basic concepts of planar science which is being applied to HPV's speaker technology creating a revolution in the way sound is reproduced.

MAD™, is an acronym for Magnetic Audio Device and is the trademark name that describes a speaker technology developed by HPV Technologies. This flat panel, planar transducer is unlike any conventional round speakers. Its unique rectangular shape creates several distinct characteristics that can’t be replicated by any traditional speaker. For more information on how speakers work, click this link: http://en.wikipedia.org/wiki/Loudspeaker

In this discussion of speakers, a planar sound source is a transducer with a flat, 2-dimensional diaphragm which produces a beam of sound (i.e. a range of frequencies) which has the same dimensions (i.e. the width and height) as the diaphragm and does not expand into larger dimensions as the sound travels away from the transducer. With a perfect planar source that is operating in a perfect environment, the sound’s volume will not decrease with distance.

Obviously even with HPV’s extraordinary technology, a perfect planar speaker is yet to be realized nor has a perfect environment been found. However, even with these limitations, HPV’s planar arrays exhibit very little sound attenuation over distance. Typically our large A-8 and A-9 planar arrays loose about 1-1.5 dB for every doubling of distance. This is compared to the ideal line arrays that have theoretically 3 dB of attenuation when throw distances double or 6 dB of attenuation per doubling of distance with conventional point source speakers.

MAD M-1 Driver

The physical structure of the MAD driver is flat and rectangular. Its diaphragm is flat measuring about 6 inches wide by 9 inches high. Having this flat form, the diaphragm is classified as a “planar” device, meaning “situated in a flat plane or having a two-dimensional characteristic”. Think of a flat piece of paper and you’ll have a picture of the diaphragm’s appearance.

All of the HPV planar systems are built around the M-1 driver. The differences between various models relates to specific performance parameters such as dispersion angles, dB-SPL output, throw distance, and tailored frequency responses which are required for each model.

... What is the difference between MAD speakers and conventional speakers?

These distinctive characteristics can be understood best with a little background in speaker physics. Traditional speakers, also referred to as drivers, are design to reproduce specific ranges of frequencies, such that woofers (i.e. large speakers) only reproduce low frequency and tweeters (i.e. small speakers) only high frequencies. For example, to generate loud bass sounds, the driver has to move (or displace) a large volume of air which requires 1) a large surface area and 2) a significant amount of excursion within the cone. The speaker cone must be very ridged and stiff so that the air does not flex the cone's surface (which creates distortion). When reproducing high frequencies, the driver's surface area can be smaller and doesn't need much excursion, however it must have very low mass and very fast transient response.

By comparison, the frequency response of a MAD driver is not constrained by its mechanical design or construction. The size and light mass of the diaphragm allows it to reproduce the full audio spectrum as it responds very quickly to fast transient sounds...while also having enough surface area to reproduce lower bass frequencies. As more drivers are grouped together, the bass response of the array is actually extended downward because the total area of all the drivers combine and behave as one large and very fast speaker.

The dispersion characteristics of MAD drivers are another aspect that is significantly different from conventional speakers. When sound emanates from round drivers, the speaker’s three dimensional shape causes the sound to radiate out in a conical pattern. Picture a rock dropped in a pond with concentric rings rippling out from a central point and you’ll get the idea. To change the sound’s natural conical dispersion into a controlled rectangular shape, it’s necessary to attach a horn assembly to the front of the driver. The horn is designed to focus and direct the sound into a predetermined horizontal and vertical pattern.

However the problem with any horn is that it can’t control the total spectrum of the sound. Some frequencies are controlled by the horn’s shape while others remain unaffected. In addition, some sounds will reflect off the inside walls of the horn causing interference inside the horn (which is a form of distortion) that can then change the driver’s original frequency response.

In contrast to the conventional round drivers, the flat two-dimensional shape of MAD’s planar driver projects sound in a much different manner. Its natural dispersion pattern is more like a beam of light (picture a laser) that does not scatter as the sound moves away from the driver. As an example, at 10 KHz the beam angle is about 10° horizontally and 7.5° in the vertical plane. Because the sound remains in this compact ray of energy, the rate of attenuation that normally occurs with speakers having a conical dispersion, is dramatically lower with a MAD driver. And since this narrow dispersion is a natural result of the diaphragm’s shape and size, rather than from an attached horn, the driver’s frequency response is not altered.

The narrow dispersion pattern on the MAD driver also becomes important when combining several drivers together. For instance in the A-8 speaker, eight drivers are arrayed next to each other to create a horizontal row. Each driver is turned about 7° relative to its adjacent neighbor, to create an arc with a nominal horizontal coverage of 60°. Because of their narrow pattern, each driver will seamlessly combine with the adjacent driver without causing interference or cancellation. This results in a very predictable and uniform horizontal coverage pattern. Since each driver is in the same vertical plane, when an A-8 speaker is stacked on top of another, the same seamless combining occurs in the vertical plane. As more rows are added, a planar array develops that can control the vertical AND horizontal pattern, a feature unavailable in conventional line arrays, which only have nominal control in the vertical dispersion plane.

Speakers come in all sizes, but the reality is that they are all designed to only reproduce a limited range of sounds. This occurs because limitations inherent in their mechanical construction physically prevent them from being able to reproduce the entire audio spectrum. Therefore all conventional drivers are built to work within limited frequency ranges. That’s the reason that you’ll never see an 18 inch woofer being used as a high frequency speaker or a 1 inch compression driver working as a woofer.

To better grasp the significance of the new MAD technology, consider the following comparisons...

MAD Transducer:

Is a full range device and can reproduce sounds from 60 Hz to 20 KHz.

The horizontal & vertical dispersion is controlled by the placement of drivers next to each other without the need of a horn assembly.

Multiple planar drivers are arranged together to create any desired horizontal and vertical dispersion pattern

Conventional Transducer:

Has a limited frequency response that is dictated by its diameter and the type of material used to build the diaphragm or cone.

A horn or wave guide must be attached to a transducer to
create a specific horizontal & vertical dispersion pattern.

Dispersion patterns are limited
to the fixed angles of horns or wave guides.